A plurality of methods of obtaining (measuring) a position of a node in a wireless communication system configured by multiple nodes are known (for example, refer to “Dynamic fine-grained localization in Ad-hoc wireless sensor networks” in the proceedings written by A. Savvides, C. C. Han and M. B. Srivastava of the International Conference on Mobile Computing and Networking (MobiCom) 2001 in Rome, Italy in July, 2001). The node includes a terminal used by a user or a sensor node. The sensor node is a terminal mounting a sensor for measuring ambient environment.
Representative node position detection methods will be described below.
A wireless communication system calculates distance between nodes based upon received signal strength (RSS) between the nodes. The wireless communication system obtains positions of the nodes by the trilateration of the calculated distance between the nodes.
In addition, the wireless communication system calculates distance between nodes based upon the time of arrival (ToA) of a signal between the nodes or time difference of arrival (TDoA). The wireless communication system obtains positions of the nodes by the trilateration of the calculated distance between the nodes.
In addition, the wireless communication system measures an angle of arrival (AoA) of a signal between nodes. The wireless communication system obtains positions of the nodes by triangulation using the measured angle of arrival.
In addition, the wireless communication system obtains a position of a node by collating with a map showing relation between received signal strength and a node position.
In addition, for a position detection method outdoors, a global positioning system (GPS) is known. GPS calculates a position of a node based upon time difference of arrival calculated utilizing a radio wave from a satellite.
In addition, a trilateration system depending upon time difference of arrival calculated utilizing a radio wave from a wireless local area network (wireless LAN) is known.
In addition, a map collation system for obtaining a position of a node depending upon a map showing relation between received signal strength between nodes and a node position is known.
In addition, a trilateration system depending upon time of arrival of an ultrasonic signal between nodes is known.
A wireless communication system that connects plural nodes at multiple stages is known. The wireless communication system obtains a position in order from a host node. The wireless communication system obtains a position of a subordinate node using the position of the host node.
In a wireless communication system that connects plural nodes at multiple stages, when a battery of one node goes flat, a position of the node cannot be obtained. Further, the wireless communication system has a problem that positions of nodes which exist in a subordinate position of the node in which the battery goes flat cannot be obtained in a chain.
A conventional type wireless communication system obtains positions of all nodes using the same position detection method. Therefore, the conventional type wireless communication system has a problem that it cannot change the position detection method according to a characteristic and a condition of a node that is an object of position detection. Characteristics of a node is a node that regards the duration of a battery as important, a node that regards measurement accuracy as important and a node that regards position detection time as important for example. The condition of the node includes the residual capacity of a battery and the output voltage of the node.
The invention is made in view of the above-mentioned problems and the object is to provide a wireless communication system that detects a position of a node using an appropriate position detection method.